Magnetic sensor with composite magnetic shield

ABSTRACT

A magneto-resistive reader includes a first magnetic shield element, a second magnetic shield element and a magneto-resistive sensor stack separating the first magnetic shield element from the second magnetic shield element. The first shield element includes two ferromagnetic anisotropic layers separated by a grain growth suppression layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/499,157, filed Jul. 8, 2009, the contents of which is herebyincorporated by reference in its entirety.

BACKGROUND

In an electronic data storage and retrieval system, a magnetic recordinghead can include a reader portion having a sensor for retrievingmagnetically encoded information stored on a magnetic medium. Magneticflux from the surface of the medium causes rotation of the magnetizationvector of a sensing layer or layers of the sensor, which in turn causesa change in the electrical properties of the sensor. The sensing layersare often called free layers, since the magnetization vectors of thesensing layers are free to rotate in response to external magnetic flux.The change in the electrical properties of the sensor may be detected bypassing a current through the sensor and measuring a voltage across thesensor. Depending on the geometry of the device, the sense current maybe passed in the plane (CIP) of the layers of the device orperpendicular to the plane (CPP) of the layers of the device. Externalcircuitry then converts the voltage information into an appropriateformat and manipulates that information as necessary to recoverinformation encoded on the disc.

A structure in contemporary magnetic read heads is a thin filmmultilayer structure containing ferromagnetic material that exhibitssome type of magnetoresistance. One magnetoresistive sensorconfiguration includes a multilayered structure formed of a nonmagneticlayer (such as a thin insulating barrier layer or a nonmagnetic metal)positioned between a synthetic antiferromagnet (SAF) and a ferromagneticfree layer, or between two ferromagnetic free layers. The resistance ofthe magnetic sensor depends on the relative orientations of themagnetization of the magnetic layers.

Magnetic read sensors have magnetic shields that to increase the spatialresolution of the read sensor by shielding the read sensor from straymagnetic fields. It is important that the magnetic domain configurationof the magnetic shield and its response to small magnetic fields fromrecording media be stable against exposure to large and nonuniformmagnetic fields in order to minimize unwanted noise registered in theread sensor. The magnetic domain configuration can be established bycontrolling the magnetic anisotropy of the ferromagnetic shieldmaterial. However, processing of the read sensor can require that theshield be exposed to strong magnetic fields at elevated temperaturesthat can reorient (e.g., cause magnetic grain growth) the magneticanisotropy of the magnetic shield in an unfavorable way.

BRIEF SUMMARY

The present disclosure relates to a magnetic sensor with a compositemagnetic shield. The present disclosure can improve the areal densitycapabilities of various types of magneto resistive (MR) readers. Thecomposite first magnetic shield provides stable anisotropy at elevatedmagnetic set and cross anneal temperatures.

In one particular embodiment, a magneto-resistive reader includes afirst magnetic shield element, a second magnetic shield element and atunneling magneto-resistive sensor stack separating the first magneticshield element from the second magnetic shield element. The first shieldelement includes two ferromagnetic anisotropic layers separated by agrain growth suppression layer. The magneto-resistive reader can be atunneling magneto-resistive reader with a TMR ratio of 100% or greater.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a front surface view of a reader including a free layerassembly having a perpendicular to the plane anisotropy and sideshields;

FIG. 2A is layer schematic diagram of an illustrative composite shield;

FIG. 2B is a layer schematic diagram of another illustrative compositeshield;

FIG. 3A-3C are layer schematic diagrams illustrating the method offorming an illustrative reader;

FIG. 4 is a flow diagram of an illustrative method of forming anillustrative reader;

FIG. 5A-5D are layer schematic diagrams illustrating the method offorming an illustrative shield element; and

FIG. 6 is a flow diagram of an illustrative method of forming anillustrative shield element.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.The definitions provided herein are to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

It is noted that terms such as “top”, “bottom”, “above, “below”, etc.may be used in this disclosure. These terms should not be construed aslimiting the position or orientation of a structure, but should be usedas providing spatial relationship between the structures. Other layers,such as seed or capping layers, are not depicted for clarity but couldbe included as technical need arises.

The present disclosure relates to a magnetic sensor with a compositemagnetic shield. The composite magnetic shield provides stableanisotropy at elevated magnetic set anneal and cross temperatures. Thecomposite magnetic shield includes two ferromagnetic layers separated bya grain growth suppression layer. The grain growth suppression layerinhibits structural changes in the ferromagnetic layers and stabilizesthe anisotropic magnetic domain structure of the shield during a hightemperature anneal. While the present disclosure is not so limited, anappreciation of various aspects of the disclosure will be gained througha discussion of the examples provided below.

FIG. 1 is a front surface view of a magneto-resistive (MR) reader 10including a composite first shield 24 in some embodiments themagneto-resistive (MR) reader is a tunneling magneto-resistive (TMR)reader. The tunneling magneto-resistive (TMR) reader 10 includes asensor stack 12 separating a second magnetic shield 14 from a firstcomposite magnetic shield 24. The sensor stack 12 includes a referencemagnetic element 34 having a reference magnetization orientation M_(R)direction a free magnetic element 30 having a free magnetizationorientation M_(F) direction substantially perpendicular (and in-plane)to the reference magnetization orientation M_(R) direction, and anon-magnetic spacer 32 layer separating the reference magnetic element34 from the free magnetic element 30. While FIG. 1 illustrates a freemagnetic element 30 having magnetization orientation M_(F) directionsubstantially perpendicular to the reference magnetization orientationM_(R) direction, it is understood that the free magnetizationorientation M_(F) direction can be substantially parallel oranti-parallel to the reference magnetization orientation M_(R)direction. Electrically insulating layer 19, 21 electrically insulatesthe second magnetic shield 14 from a first composite magnetic shield 24.

In the embodiment shown, free magnetic element 30 is on the top ofsensor stack 12 and reference magnetic element 34 is on the bottom ofsensor stack 12. It will be appreciated that sensor stack 12 mayalternatively include reference magnetic element 34 on the top of sensorstack 12 and free magnetic element 30 on the bottom of sensor stack 12.

Free magnetic element 30 is a single or a composite or multiple layerstructure having a magnetization M_(F) that rotates in response to anexternal magnetic field. In many embodiments, the sensor stack 12 sensesmagnetic flux from a magnetic media. In tunneling magneto-resistive(TMR) reader embodiments, the sensor stack 12 is a tunneling magnetoresistive type (TMR) sensor where the reference magnetic element 34 andthe free magnetic element 30 are ferromagnetic layers separated by aninsulating spacer layer 32 that is thin enough (e.g., 1 to 5 nanometersthick) to allow electrons to tunnel from one ferromagnetic layer to theother ferromagnetic layer.

Spacer layer 32 is a nonmagnetic insulting layer disposed between freemagnetic element 30 and reference magnetic element 34. In manyembodiments, spacer layer 32 is a non-magnetic, insulative orsemi-conductive material, such as oxides formed of Mg, Al, Hf, or Ti. Insome embodiments the spacer layer 32 is MgO.

Reference magnetic element 34 has a fixed magnetization direction M_(R)that is in-plane with the layer or layers of magnetic element 34.Magnetization direction M_(F) of free magnetic element 30 is eitherperpendicular to fixed magnetization direction M_(R) in a quiescentstate or parallel or anti-parallel to fixed magnetization directionM_(R) in a quiescent state. Reference magnetic element 34 may be asingle ferromagnetic layer having an anisotropically definedmagnetization direction. Reference magnetic element 34 may also includevarious combinations of layers to provide magnetization M_(R) having afixed direction, such as a ferromagnetic pinned layer with anantiferromagnetic pinning layer, a synthetic ferromagnetic pinned layer(i.e., two ferromagnetic layers coupled by a nonmagnetic metal, such asRu), or a synthetic ferromagnetic pinned layer coupled to anantiferromagnetic pinning layer. Ferromagnetic layers of reference layerassembly 34 may be made of a ferromagnetic alloy, such as CoFe, NiFe, orNiFeCo, and the antiferromagnetic layer may be made of PtMn, IrMn, NiMn,or FeMn.

In operation, a sense current is passed through sensor stack 12 viashields 14 and 24 (which can also function as electronic leads in someembodiments) such that the sense current passes perpendicular to theplane of the layer or layers of sensor stack 12. As magnetization M_(F)rotates in response to external magnetic fields, the resistance ofsensor stack 12 changes as a function of the angle betweenmagnetizations M_(F) and M_(R). The voltage across sensor stack 12 ismeasured between leads/shields 14 and 24 by external circuitry (notshown) to detect changes in resistance of sensor stack 12.

Portions of the sensor stack 12 require annealing to set a magnetizationdirection therein. Tunneling magneto resistive type sensor stack 12design has shown that higher annealing temperatures such as, 300 degreescentigrade or greater, or 340 degrees centigrade or greater, or 390degrees centigrade or greater, for example, improves the TMR ratio % ofthe sensor stack 12. The high temperature anneals can produce atunneling magneto resistive type sensor stack 12 having a TMR ratio of100% or greater, or 200% or greater, or 300% or greater. The TMR(tunneling magneto-resistive) ratio % is derived from the followingequation (1):TMR ratio (%)=(Rmax−Rmin)/Rmax×100  (1)Where Rmax and Rmin are the resistance values obtained when applying acurrent through the sensor stack in a parallel (low resistance state)and anti-parallel (high resistance state). Increasing the TMR ratioimproves the sensor stack sensitivity and reliability.

Since the tunneling magneto resistive type sensor stack 12 is depositedon the composite first shield 24, the composite first shield 24 has toprovide stable anisotropy at the higher anneal temperatures that areneeded to provide the sensor stack 12 that possess a higher TMR ratiopercentage. The composite first shield 24 described herein providesstable anisotropy at the higher anneal temperatures.

The composite first shield 24 includes two ferromagnetic anisotropiclayers 26, 27 separated by a grain growth suppression layer 25. Thegrain growth suppression layer 25 inhibits diffusion, defect mobility,and grain crystallization during magnetic annealing of themagneto-resistive reader 10. The grain growth suppression layer 25 has athickness of less than 100 Angstroms or 50 Angstroms or less, or athickness in a range from 5 to 50 Angstroms. In many embodiments, theoverall thickness of the composite first shield 24 is about onemicrometer and in many embodiments the thickness of each of the twoferromagnetic anisotropic layers 26, 27 is about equal.

In some embodiments the grain growth suppression layer 25 isnon-magnetic. In some embodiments the grain growth suppression layer 25is magnetic. In illustrative embodiments, the grain growth suppressionlayer 25 is Ru, Ta, Nb, Zr, or Hf and the two ferromagnetic anisotropiclayers 26, 27 are NiFe. In many embodiments, the grain growthsuppression layer 25 is Ru or Ta and the two ferromagnetic anisotropiclayers 26, 27 are NiFe.

FIG. 2A is layer schematic diagram of an illustrative composite firstshield 24. The composite first shield 24 includes two ferromagneticanisotropic layers 26, 27 separated by a grain growth suppression layer25, as described above. In some embodiments the grain growth suppressionlayer 25 is non-magnetic. In some embodiments the grain growthsuppression layer 25 is magnetic. The composite first shield 24 canfurther include an optional hard magnetic layer 28. The hard magneticlayer 28 can be formed of any useful magnetic material that has anability to magnetically couple to the bottom of the composite shieldlayers and have a magnetic coercivity high enough to withstandmagnetization reversal from media and stray fields during operation.

FIG. 2B is a layer schematic diagram of another illustrative compositefirst shield 24. The composite first shield 24 includes threeferromagnetic anisotropic layers 26, 27, 23 separated by grain growthsuppression layers 25, 29, as described above. In some embodiments thegrain growth suppression layer 25, 29 is non-magnetic. In someembodiments the grain growth suppression layer 25, 29 is magnetic. Thecomposite first shield 24 further can include a hard magnetic layer likein FIG. 2A. The hard magnetic layer 28 can be formed of any usefulmagnetic material.

FIG. 3A-3C are layer schematic diagrams illustrating the method offorming an illustrative tunneling magneto-resistive (TMR) reader 10.FIG. 4 is a flow diagram of an illustrative method of forming anillustrative tunneling magneto-resistive (TMR) reader. The methodincludes depositing a first shield element 24 on a substrate 5. Thefirst shield element 24 can be sputter deposited using semiconductorfabrication techniques. The first shield element 24 includes twoferromagnetic anisotropic layers 27, 26 separated by a grain growthsuppression layer 25 at block 101. The first shield element 24 isdescribed above.

Then the method includes annealing the first shield element 24 at amagnetic set anneal temperature to form a set annealed first shield atblock 102. A magnetic field is applied to the first shield element 24 atan elevated temperature to set the magnetic orientation of the at leastone ferromagnetic layer 27, 26 of the first shield element 24. In manyembodiments the magnetic set anneal temperature is greater than 350degrees centigrade, or greater than 390 degrees centigrade, or greaterthan 440 degrees centigrade. As described above, the grain growthsuppression layer 25 inhibits grain growth and improves the anisotropyof the first shield element 24.

Then the method includes depositing a tunneling magneto-resistive sensorstack 12 on the annealed first shield 24 at block 103 The tunnelingmagneto-resistive sensor stack 12 includes a reference magnetic element34, a free magnetic element 30, and a non-magnetic spacer 32 layerseparating the reference magnetic element 34 from the free magneticelement 30. The tunneling magneto-resistive sensor stack 12 is describedabove and can be sputter deposited using semiconductor fabricationtechniques.

Then the tunneling magneto-resistive sensor stack 12 is annealed at amagnetic cross set anneal temperature to form a cross set annealedtunneling magneto-resistive sensor stack at block 104. A magnetic fieldis applied to the tunneling magneto-resistive sensor stack 12 at anelevated temperature to set the magnetic orientation of the at least oneferromagnetic layer 30, 34 of the tunneling magneto-resistive sensorstack 12. In many embodiments the cross set magnetic field isperpendicular to the magnetic set magnetic field. The magnetic cross setanneal temperature is below the set annealing temperature of the firstshield element 24 so as not disturb the magnetic orientation of thefirst shield element 24 and above the blocking temperature of theantiferromagnet in the stack so the reference layer is pinned when itcools after annealing. In many embodiments, the magnetic cross setanneal temperature is greater than 350 degrees centigrade, or greaterthan 390 degrees centigrade. A second shield element 14 is thendeposited on the cross set annealed tunneling magneto-resistive sensorstack 12 at block 105, to form the tunneling magneto-resistive (TMR)reader 10.

FIG. 5A-5D are layer schematic diagrams illustrating the method offorming an illustrative first shield element. FIG. 6 is a flow diagramof an illustrative method of forming an illustrative first shieldelement. The method includes depositing a first shield element 24. Thefirst shield element 24 including two ferromagnetic anisotropic layers27, 26 separated by a grain growth suppression layer 25, and annealingthe first shield element 24 to form a set annealed first shield, asdescribed above. An exposed surface of the first shield element 24 isthen polished to form a smooth exposed first shield surface, utilizingsemiconductor fabrication techniques. The polishing step removes a minoramount of layer being polished. For example, the polishing step removesless than 2% or less than 1% of the ferromagnetic layer being polished.

The structure of the first shield element 24 can be defined by anyuseful method, such as patterning by photolithography and then etching,for example. The patterning can be preformed following the deposing stepof bock 201. The resulting structure is described as a patterned firstshield element 24 below.

In many embodiments, a chemical mechanical polishing (CMP) stop layer 50is then deposited on the smooth exposed first shield surface at block201. The CMP stop layer 50 can be any useful CMP stop material such aschromium or a-carbon, for example. In many embodiments this structure isthen patterned to form the desired first shield element dimensions,utilizing semiconductor fabrication techniques. In other embodiments, achemical mechanical polishing (CMP) stop layer 50 is not deposited.

An insulating material 60 is deposited about the patterned first shieldelement 24 at block 202. The insulating material can be any usefulelectrically insulating material such as metal oxides or semiconductoroxides, for example. The insulating material 60 can encapsulate thepatterned first shield element 24.

Then the method includes removing insulating material 60 by chemicalmechanical polishing down to the chemical mechanical polishing stoplayer 50 at block 203. The CMP method step forms a planar surface ofinsulating regions and CMP stop layer regions. Then the chemicalmechanical polishing stop layer 50 is removed at bock 204. Then thesensor stack can be deposited on smooth exposed surface of the firstshield element as described above.

This method provides layer thickness control of the top ferromagneticlayer of the composite first shield. Very little of the topferromagnetic layer is removed during the CMP process and the smoothpolish method step provides a smooth surface for depositing the sensorstack and improves the sensor stack uniformity during deposition.

Thus, embodiments of the MAGNETIC SENSOR WITH COMPOSITE MAGNETIC SHIELDare disclosed. The implementations described above and otherimplementations are within the scope of the following claims. Oneskilled in the art will appreciate that the present disclosure can bepracticed with embodiments other than those disclosed. The disclosedembodiments are presented for purposes of illustration and notlimitation, and the present invention is limited only by the claims thatfollow.

What is claimed is:
 1. A method of forming a magneto-resistive readercomprising: depositing a first shield element, the first shield elementcomprising two ferromagnetic anisotropic layers separated by a graingrowth suppression layer; annealing the first shield element at amagnetic set anneal temperature to form a set annealed first shield;depositing a magneto-resistive sensor stack on the annealed firstshield; annealing the magneto-resistive sensor stack at a magnetic crossset anneal temperature to form a cross set annealed magneto-resistivesensor stack; and depositing a second shield element on the cross setannealed magneto-resistive sensor stack.
 2. A method according to claim1, wherein the magnetic set anneal temperature is greater than 390degrees centigrade.
 3. A method according to claim 1, wherein themagnetic cross set anneal temperature is greater than 300 degreescentigrade.
 4. A method according to claim 1, wherein the grain growthsuppression layer has a thickness of less than 100 Angstroms.
 5. Amethod according to claim 4, wherein the grain growth suppression layeris non-magnetic.
 6. A method according to claim 1, wherein the magneticcross set anneal step comprises applying a magnetic field that isperpendicular a magnetization orientation direction of the first shieldelement.
 7. A method according to claim 1, wherein the magnetic crossset anneal temperature less than the magnetic set anneal temperature. 8.A method according to claim 1, wherein the magneto-resistive sensorstack is a tunneling magneto-resistive reader having a TMR ratio of 200%or greater.
 9. A method according to claim 1, wherein the ferromagneticanisotropic layers comprise NiFe and the grain growth suppression layercomprises Ru.
 10. A method according to claim 1, wherein theferromagnetic anisotropic layers comprise NiFe and the grain growthsuppression layer comprises or Ta.
 11. A method according to claim 1,wherein the ferromagnetic anisotropic layers comprise NiFe and the graingrowth suppression layer comprises Nb, Zr or Hf.
 12. A method accordingto claim 1, wherein the two ferromagnetic anisotropic layers have aboutequal thicknesses.
 13. A method according to claim 1, wherein the graingrowth suppression layer inhibits diffusion, defect mobility, and graincrystallization during magnetic annealing of the magneto-resistivereader.
 14. A method according to claim 1, wherein the first magneticshield element further comprises a third ferromagnetic anisotropiclayer, and a second grain growth suppression layer is located betweenthe third ferromagnetic anisotropic layer and the second ferromagneticanisotropic layer.
 15. A method of forming a first shield for atunneling magneto-resistive reader comprising: depositing a first shieldelement, the first shield element comprising two ferromagneticanisotropic layers separated by a grain growth suppression layer;annealing the first shield element at a magnetic set anneal temperatureto form a set annealed first shield; polishing an exposed surface of thefirst shield element to form a smooth exposed first shield surface;depositing a chemical mechanical polishing stop layer on the smoothexposed first shield surface; depositing an insulating material aboutthe first shield element; removing insulating material by chemicalmechanical polishing down to the chemical mechanical polishing stoplayer; removing the chemical mechanical polishing stop layer, forming apolished first shield element; depositing a magneto-resistive sensorstack on the polished first shield; annealing the magneto-resistivesensor stack at a magnetic cross set anneal temperature to form a crossset annealed magneto-resistive sensor stack.
 16. A method according toclaim 15, wherein the polishing step removes less than 2% of theferromagnetic anisotropic layer being polished.
 17. A method accordingto claim 15, wherein the polishing step removes less than 1% of theferromagnetic anisotropic layer being polished.
 18. A method accordingto claim 15, wherein the magneto-resistive sensor stack is a tunnelingmagneto-resistive reader having a TMR ratio of 100% or greater.
 19. Amethod according to claim 15, wherein the magneto-resistive sensor stackis a tunneling magneto-resistive reader having a TMR ratio of 100% orgreater.